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<document xmlns="http://cnx.rice.edu/cnxml" xmlns:m="http://www.w3.org/1998/Math/MathML" xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns:bib="http://bibtexml.sf.net/" id="m10108">

  <name>Discrete-Time Fourier Transform (DTFT)</name>

  <metadata>
  <md:version>2.10</md:version>
  <md:created>2001/06/18</md:created>
  <md:revised>2005/03/23 15:40:21 US/Central</md:revised>
  <md:authorlist>
      <md:author id="richb">
      <md:firstname>Richard</md:firstname>
      <md:othername>G.</md:othername>
      <md:surname>Baraniuk</md:surname>
      <md:email>richb@rice.edu</md:email>
    </md:author>
  </md:authorlist>

  <md:maintainerlist>
    <md:maintainer id="jrom">
      <md:firstname>Justin</md:firstname>
      
      <md:surname>Romberg</md:surname>
      <md:email>jrom@rice.edu</md:email>
    </md:maintainer>
    <md:maintainer id="mselik">
      <md:firstname>Melissa</md:firstname>
      
      <md:surname>Selik</md:surname>
      <md:email>mselik@alumni.rice.edu</md:email>
    </md:maintainer>
    <md:maintainer id="richb">
      <md:firstname>Richard</md:firstname>
      <md:othername>G.</md:othername>
      <md:surname>Baraniuk</md:surname>
      <md:email>richb@rice.edu</md:email>
    </md:maintainer>
    <md:maintainer id="rars">
      <md:firstname>Ricardo</md:firstname>
      <md:othername>Anthony</md:othername>
      <md:surname>Radaelli-Sanchez</md:surname>
      <md:email>ricky@alumni.rice.edu</md:email>
    </md:maintainer>
    <md:maintainer id="mariyah">
      <md:firstname>Mariyah</md:firstname>
      
      <md:surname>Poonawala</md:surname>
      <md:email>mariyah@rice.edu</md:email>
    </md:maintainer>
    <md:maintainer id="prash">
      <md:firstname>Prashant</md:firstname>
      
      <md:surname>Singh</md:surname>
      <md:email>prash@ece.rice.edu</md:email>
    </md:maintainer>
  </md:maintainerlist>
  
  <md:keywordlist>
    <md:keyword>continuous frequency</md:keyword>
    <md:keyword>discrete time</md:keyword>
    <md:keyword>DTFT</md:keyword>
    <md:keyword>fourier transform</md:keyword>
  </md:keywordlist>

  <md:abstract>Details the discrete-time fourier transform.</md:abstract>
</metadata>

  <content>

    <equation id="eqn1">
      <name>Discrete-Time Fourier Transform</name>
      <m:math>
	<m:apply>
	  <m:eq/>
	  <m:apply>
	    <m:ci type="fn">X</m:ci>
	    <m:ci>ω</m:ci>
	  </m:apply>
	  <m:apply>
	    <m:sum/>
	    <m:bvar>
	      <m:ci>n</m:ci>
	    </m:bvar>
	    <m:lowlimit>
	      <m:apply>
		<m:minus/>
		<m:infinity/>
	      </m:apply>
	    </m:lowlimit>
	    <m:uplimit>
	      <m:infinity/>
	    </m:uplimit>
	    <m:apply>
	      <m:times/>
	      <m:apply>
		<m:ci type="fn">x</m:ci>
		<m:ci>n</m:ci>
	      </m:apply>
	      <m:apply>
		<m:exp/>
		<m:apply>
		  <m:minus/>
		  <m:apply>
		    <m:times/>
		    <m:imaginaryi/>
		    <m:ci>ω</m:ci>
		    <m:ci>n</m:ci>
		  </m:apply>
		</m:apply>
	      </m:apply>
	    </m:apply>
	  </m:apply>
	</m:apply>
      </m:math>
    </equation>

    <equation id="eqn2">
      <name>Inverse Discrete-Time Fourier Transform</name>
      <m:math>
	<m:apply>
	  <m:eq/>
	  <m:apply>
	    <m:ci type="fn">x</m:ci>
	    <m:ci>n</m:ci>
	  </m:apply>
	  <m:apply>
	    <m:times/>
	    <m:apply>
	      <m:divide/>
	      <m:cn>1</m:cn>
	      <m:apply>
		<m:times/>
		<m:cn>2</m:cn>
		<m:pi/>
	      </m:apply>
	    </m:apply>
	    <m:apply>
	      <m:int/>
	      <m:bvar>
		<m:ci>ω</m:ci>
	      </m:bvar>
	      <m:lowlimit>
		<m:cn>0</m:cn>
	      </m:lowlimit>
	      <m:uplimit>
		<m:apply>
		  <m:times/>
		  <m:cn>2</m:cn>
		  <m:pi/>
		</m:apply>
	      </m:uplimit>
	      <m:apply>
		<m:times/>
		<m:apply>
		  <m:ci type="fn">X</m:ci>
		  <m:ci>ω</m:ci>
		</m:apply>
		<m:apply>
		  <m:exp/>
		  <m:apply>
		    <m:times/>
		    <m:imaginaryi/>
		    <m:ci>ω</m:ci>
		    <m:ci>n</m:ci>
		  </m:apply>
		</m:apply>
	      </m:apply>
	    </m:apply>
	  </m:apply>
	</m:apply>
      </m:math>
    </equation>

    <section id="sect1">
      <name>Relevant Spaces</name>
      <para id="para1">
	The <cnxn strength="7" document="m10247"> Discrete-Time Fourier 
        Transform </cnxn>maps infinite-length,
	discrete-time signals in
	<m:math>
	  <m:ci><m:msup>
	      <m:mi>l</m:mi>
	      <m:mn>2</m:mn>
	    </m:msup></m:ci>
	</m:math>
	to finite-length (or 
	<m:math>
	      <m:apply>
		<m:times/>
		<m:cn>2</m:cn>
		<m:pi/>
	      </m:apply>
	</m:math>-periodic), continuous-frequency
	signals in
	<m:math>
	  <m:ci><m:msup>
	      <m:mi>L</m:mi>
	      <m:mn>2</m:mn>
	    </m:msup></m:ci>
	</m:math>.
      </para>

      <figure id="fig1">
	<media type="image/png" src="DTFT1.png"/>
	<caption>
	  Mapping 
	  <m:math>
	    <m:apply>
	      <m:ci type="fn"><m:msup>
		  <m:mi>l</m:mi>
		  <m:mn>2</m:mn>
		</m:msup></m:ci>
	      <m:integers/>
	    </m:apply>
	  </m:math>
	  in the time domain to
	  <m:math>
	    <m:apply>
	      <m:ci type="fn"><m:msup>
		  <m:mi>L</m:mi>
		  <m:mn>2</m:mn>
		</m:msup></m:ci>
	      <m:interval closure="closed-open">
		<m:cn>0</m:cn>
		<m:apply>
		  <m:times/>
		  <m:cn>2</m:cn>
		  <m:pi/>
		</m:apply>
	      </m:interval>
	    </m:apply>
	  </m:math>
	  in the frequency domain.
	</caption>
      </figure>
    </section>

  </content>
</document>
